Two Plus Two Older Archives  

Go Back   Two Plus Two Older Archives > General Gambling > Probability
FAQ Community Calendar Today's Posts Search

Reply
 
Thread Tools Display Modes
  #11  
Old 08-05-2002, 01:16 AM
Guest
 
Posts: n/a
Default Why are people using formulas?



I thought it was funny that the early reponses decided to show their answers determined by formulas.


They must have skipped over the first sentence in David's post: Again I am trying to get you to think, not blindly use formulas.


They must have missed the point of the exercise. I'll go with 25% too.



Reply With Quote
  #12  
Old 08-05-2002, 01:19 AM
Guest
 
Posts: n/a
Default 3/4 or 75%



If fair coins turn up HH 1/4 of the time that means the other 3/4 of the time it came up HH it would be the double headed coin.


Just a guess since DS asked for logic and not formulas.


Flame away.
Reply With Quote
  #13  
Old 08-05-2002, 01:27 AM
Guest
 
Posts: n/a
Default Re: Of Course That\'s Wrong



4:3= 4/7 = the chances you picked the bad coin
Reply With Quote
  #14  
Old 08-05-2002, 01:41 AM
Guest
 
Posts: n/a
Default ...or maybe 80%....??



another theory although most likely incorrect.


P(HH for fair coin) = .25

P(HH for unfair) = 1.00


P(unfair HH) divided by P(fair + unfair coins) = .80


1.00/1.25 = 0.80 or 80%


again flame away.
Reply With Quote
  #15  
Old 08-05-2002, 01:49 AM
Guest
 
Posts: n/a
Default Re: double random (1/4) or 1/2 *NM*




Reply With Quote
  #16  
Old 08-05-2002, 01:54 AM
Guest
 
Posts: n/a
Default Re: double - after reading others



once you flip a coin and get a side, then if you flip it again theres a 50% chance you get the same side in a fair coin, or 100% in a double sided coin.


thats why i say its double fair chance of 1/4.


so 1/2.


but now i see it wasnt a double sided coin but a double headed coin. ugh. too much scotch i guess


brad
Reply With Quote
  #17  
Old 08-05-2002, 01:58 AM
Guest
 
Posts: n/a
Default Re: ...or - weighted average?



(3(.25) + 1(1) )/ 4


=


1.75/4


= 43.75%


?
Reply With Quote
  #18  
Old 08-05-2002, 03:17 AM
Guest
 
Posts: n/a
Default You\'re not allowed to use Petriv\'s book either. *NM*




Reply With Quote
  #19  
Old 08-05-2002, 03:23 AM
Guest
 
Posts: n/a
Default Done by Logic



i think there are two events here


picking


and flicking


(you can easily remember this "formula" by thinking of dynasty's nose)


picking is not affected by flicking


so the chances that you picked the double-headed coin are 1 in 4


once you've picked it it doesn't really matter if you flick ten heads in a row - although unusual, it's already on your finger
Reply With Quote
  #20  
Old 08-05-2002, 03:31 AM
Guest
 
Posts: n/a
Default Re: Do This by Logic



We pick the bad coin 1/4 of the time. We get 2 heads 1/4 of the time when we pick the 3 good coins, and all the time when we pick the bad coin, so the total probability that we get 2 heads is (1/4)(3/4) + (1/4)(1) = 7/16. So the fraction of the time we have the bad coin when we get 2 heads is (1/4)/(7/16) = 4/7.
Reply With Quote
Reply


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 12:56 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.